In recent years, with the miniaturization of semiconductor devices, the representative dimensions of their basic constituent elements—transistors—have reached the level of less than or equal to several tens of nanometers. Additionally, in order to achieve higher densities and improvement in element capability, in place of the conventional planar transistor (flat surface) structure, three-dimensional (3D) structures are being employed as well.
Regarding the forming of the source/drain of transistors, in general, first, dopants are introduced to the desired depth of the semiconductor layer using ion implantation, after which, heat treatment (active annealing) is carried out. That is, with the introduction of dopants, the surface of the single crystal semiconductor layer is amorphized, and with active annealing, the amorphous region is recrystallized and implant defects are ameliorated. Generally, for this active annealing, a few seconds of RTA (Rapid Thermal Annealing) at around 1000° C. is performed.
On the other hand, from the perspective of miniaturization, the processing width of the semiconductor chip that has a three-dimensional structure must be scaled down. For this reason, the area of the amorphous/single crystal interface, which becomes the crystal nucleus when changing the amorphous region back to a single crystal, becomes relatively small. Under these circumstances, before the entire amorphous region returns back to a single crystal, minute crystal nuclei come into being at random locations due to heat, and crystal growth occurs with those crystal nuclei as the points of origin.
Thus, especially in the case of fine three-dimensional structures, due to active annealing, the amorphized region grows into a polycrystalline semiconductor instead of a single crystal. In the case that it is polycrystallized, its own resistivity rises while the contact resistance between the polycrystalline layer and the metal wiring rises by over three-digits, and the parasitic resistance that is formed in series in the semiconductor device increases, causing degradation in the device characteristics.
In this way, with conventional active annealing, due to the miniaturization of semiconductor chips, crystal defects of the semiconductor layers by the introduction of dopants could not be sufficiently recovered.